The present invention relates to a wheel hub unit for a vehicle. The present invention also relates to a vehicle being provided with a wheel hub unit.
The invention is applicable on working machines within the fields of industrial construction machines or construction equipment; in particular wheel loaders and articulated haulers. Although the invention will be described with respect to a wheel loader, the invention is not restricted to this particular vehicle, but may also be used in other working machines, such as excavators and backhoe loaders. It may also be used in e.g. trucks, buses or cars.
Vehicles, for example wheel loaders, today are often provided with a final drive comprising a hub-mounted reduction gear. The hub-mounted reduction gear can be provided in the form of a hub unit and is provided in the wheel which is intended to be driven. The wheel hub unit may typically comprise at least one planetary gear set with an integral brake, and a bearing. The sun gear of the planetary gear set is rotationally locked to and driven by a drive shaft connected to the vehicle's drive source. The sun gear is in engagement with, and drives, planet gears which are arranged between the sun gear and a ring gear. The bearing is provided between the stationary ring gear of the planetary gear set and the rim. The planet carrier is fixedly connected to the rim, and thereby drives the wheel. An example of such a wheel hub unit is provided in EP 1 899 619.
There is a general desire in the industry to develop the drive systems of the vehicles, including i.a. the wheel hub units. The wheel hub units may be improved e.g. by adding further reduction gears or by adding electric motors to them, thereby enabling electric or hybrid drive of the vehicle. However, the size of the rim is usually fixed for the specific type of vehicle, and the wheel hub unit should preferably be able to fit in the rim. If portions of the wheel hub unit extend outside the rim, there is a risk that the ground clearance of the vehicle is compromised.
It is desirable to provide a wheel hub unit which may contain more and/or larger components, as compared to the prior art, and still fit into a rim of a specific size.
The wheel hub unit according to the present invention comprises at least one planetary gear set, comprising a sun gear, one set of planet gears, a carrier, and a ring gear, wherein each of the planet gears of the set of planet gears is provided with engagement means adapted for engagement with corresponding engagement means of the ring gear, and wherein said engagement is provided at an engagement area where said engagement means of the planet gears overlap said engagement means of the ring gear. The wheel hub unit also comprises a bearing, comprising an inner bearing ring, an outer bearing ring and rolling elements. The inner bearing ring constitutes the ring gear of the planetary gear set, wherein a center of each of the respective rolling elements is axially displaced in relation to said engagement area.
With axially displaced is meant to understand that a straight radially extending imaginary line which intersects an axial center line of the wheel hub unit perpendiculary and intersects the center of one of said rolling elements is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendiculary and intersects the portion of the engagement area that is closest to said rolling element. As is also understood, the imaginary lines that extend perpendicularly from the axial center of the wheel hub unit, and intersect the center of a rolling element of a bearing and the engagement area of the planetary gear set, respectively, are parallel with each other.
By axially displacing the rolling elements of the bearing and the engagement area where said engagement means of the planet gears overlap said engagement means of the ring gear engagement, the available space along the axial length of the wheel hub unit is better utilized, and the radial limitation is thereby to at least some extent handled. A benefit of axially displacing these two parts of the wheel hub unit is that the ring gear/inner bearing ring require a certain material thickness in order to reliably fulfill it tasks. It is therefore usually not acceptable to reduce the material thickness in order to make it fit within the constraints of a rim of a specific size. Reducing the material thickness may also not always be enough in order to fit a planetary gear set of a desired size radially inwards of a bearing. By the inventive axial displacement, the required material thickness may be achieved within the specified size constraints and the planetary gear set may be made larger and still be able to be used within a rim of a specific size. According to this first aspect, it is not required that there is no axial overlap between the rolling elements and the engagement area. Instead, it is only required that the portion of the engagement area being closest to the rolling elements is displaced in the axial direction in relation to the center of the rolling elements.
According to one exemplary embodiment, the rolling elements are axially displaced in relation to the engagement area of the planet gear engagement means and the ring gear engagement means, such that the entire rolling elements are arranged axially outside of the engagement area.
Hence, in this embodiment, a straight imaginary line that intersects the axial center line of the wheel hub unit perpendicularly and intersects one of said rolling elements at the portion of the rolling element being closest to the engagement area is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendicularly and intersects the portion of the engagement area that is closest to said rolling element.
Hence, according to this aspect of the present invention, the engagement area is ax tally distanced in relation to the rolling elements of the bearing, such that no axial overlap is present between the engagement area and the rolling elements of the bearing. By that, it is possible to provide for a ring gear/inner bearing ring having an even larger material thickness as compared to the first embodiment of the present invention. It may even be conceivable with a planetary gear set in which the root diameter of die ring gear is larger than the diameter of the raceway of the inner bearing ring. Hence, a larger planetary gear set may be provided within a rim of a specific size.
According to one exemplary embodiment, the bearing is a double-row bearing. According to this exemplary embodiment, the rolling elements of the double-row bearing are axially displaced in relation to the engagement area of the planet gear engagement means and the ring gear engagement means, such that both rolling elements in each pair of rolling elements are arranged axially outside of the engagement area.
Hence, a straight imaginary line that intersects the axial center line of the wheel hub unit perpendicularly and intersects a rolling element in the row of rolling elements that is closest to the engagement area is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendicularly and intersects the portion of the engagement area that is closest to said rolling element. Hence, according to this embodiment, the engagement area is axially displaced in relation the rolling elements being closest to the engagement means. As for the embodiment described above, a configuration according to this embodiment allows for the possibility to provide a larger planetary gear set.
According to an exemplary embodiment, the engagement means of the planet gears are provided in the form of teeth. According to one exemplary embodiment, corresponding teeth are provided on an inward facing surface of the ring gear, as seen in the radial direction of the wheel hub unit.
According to one exemplary embodiment, the wheel hub unit has an axial extension with an inner end being the end that is adapted to be connected to a vehicle, and an outer end being the end that is adapted to be connected to a rim for holding a wheel.
According to one exemplary embodiment, said inner bearing ring comprises a flange which extends in the axial direction of said wheel hub unit, and wherein the engagement means of the ring gear are provided on said flange. Providing the engagement means of the ring gear on a flange extending in the axial direction of the wheel hub unit is a beneficial way of axially distancing the engagement area from the rolling elements of the bearing.
According to one exemplary embodiment, the engagement area is provided closer to the outer end than said rolling elements of the bearing, as seen in the axial direction of the wheel hub unit. Hence, the engagement area is provided further axially away from where the wheel hub unit is connected to the vehicle body, as compared to where the rolling elements are provided. They do however not extend outside the outermost portion of the rim or the wheel when the wheel hub unit is fitted to a rim. In order to provide for a vehicle with good ground clearance, it is beneficial to provide all parts of the wheel hub unit within the rim or wheel.
According to one exemplary embodiment, the inner ring of the bearing is a split inner ring comprising two parts. A split inner ring comprises at least two parts that are connected through a suitable connecting element. Such a connecting element may e.g. be a bolt or screw. Providing the inner ring of the bearing as a split inner ring is beneficial in terms of simplified production whiles it at the same time provides for a sufficiently strong and robust bearing ring.
According to one exemplary embodiment, both parts of the split inner bearing ring are in contact with the rolling elements of the bearing. In other words, the bearing race is provided in a space defined by both parts of the inner bearing ring.
According to one exemplary embodiment, a first pan of the two parts of the split inner bearing ring constitutes the ring gear of the planetary gear set. Hence, the engagement means of the ring gear is provided on only one of the parts of split inner bearing ring.
According to one exemplary embodiment, said first part of the split inner bearing ring is provided closer to the outer end of the wheel hub unit than said other pan of the split inner bearing ring, as seen in the axial direction of the wheel hub unit. It is beneficial to provide the engagement means at the outer pan of the split inner bearing ring as the engagement means are intended to be in meshed engagement with the engagement means of the planetary gear set.
According to one exemplary embodiment, said wheel hub unit comprises a drive shaft, which extends along at least a portion of the axial center line of said wheel hub unit. The drive shaft may beneficially be connected to a drive source, such as e.g. an electrical motor, a hydraulic drive or an ICE.
According to one exemplary embodiment, said drive shaft is, directly or indirectly, drivingly connected to the sun gear of said at least one planetary gear set.
According to one exemplary embodiment, said wheel hub unit further comprises an electric machine as a drive source for driving the sun gear.
According to one exemplary embodiment, said wheel hub unit comprises at least two planetary gear sets coupled in series between the electric machine and the wheel hub. According to one exemplary embodiment, the wheel hub unit is provided with a gear shifting device. According to one exemplary embodiment, the gear shifting device comprises at least one further planetary gear set, and said gear shifting device is adapted for connecting and disconnecting, respectively, the planet gears of said one further planetary gear set from being driving) y connected to an electric machine. The present invention may be especially beneficial when more components, such as further planetary gear sets and an electric machine shall be fitted in the wheel hub unit.
According to one exemplary embodiment, said wheel hub unit comprises at least two planetary gear sets coupled in series, wherein one of said at least two planetary gear sets constitutes said at least one planetary gear set. Hence, it is not necessary that the engagement areas of all planetary gear sets of a wheel hub unit are axially displaced in relation to the rolling elements of a bearing of a wheel hub unit. The purpose of the present invention may well be achieved if the engagement areas of one of two or more planetary gear sets are axially displaced in relation to die rolling elements of the bearing.
According to one exemplary embodiment, the planetary gear set having the largest diameter of the at least two planetary gear sets constitutes said at least one planetary gear set. According to this exemplary embodiment, when the wheel hub unit comprises more than one planetary gear set, it is the planetary gear set with the largest diameter whose engagement areas are axially displaced in relation to the rolling element of the bearing. With diameter is meant to understand the diameter of the ring gear of the planetary gear set. As the purpose of the present invention is to provide for a wheel hub unit which may contain more and/or larger components and still fit into a rim of a specific size, the invention may be more beneficial if it is the planetary gear set with the largest diameter that is axially displaced. Hence, one planetary gear set having a smaller diameter may be provided at the same axial position as the bearing and there may still be sufficient material thickness for the ring gear/inner bearing ring.
According to one exemplary embodiment, a root diameter of the ring gear is in the range of 95-110% of an inner raceway diameter of the inner bearing ring. By axially displacing the engagement area of the engagement means of the ring gear and engagement means of the planet gears and the rolling elements of the bearing, it is possible to provide for a larger planetary gear set than what was possible with the prior art. Therefore, it is possible to provide for a wheel hub unit in which the ring gear has a root diameter which is 95% or more of the diameter of the inner raceway of the bearing. In other words, the diameter of the ring gear as measured at the bottom of the gears may be 95% or more of the distance between the radially innermost parts of two rolling elements of the bearing being positioned opposite each other. By the axial displacement, it is even possible to provide planetary gear sets having a larger diameter, for example up to 110%, than the diameter of the bearing, even though the inner bearing ring constitutes the ring gear.
According to one exemplary embodiment, a root diameter of the ring gear is in the range of 95-100% of an inner raceway diameter of the inner bearing ring. According to this exemplary embodiment, the root diameter of the ring gear is at most the same as the inner raceway diameter of the inner bearing ring. It is however larger than what would have been possible if the planet gears and the rolling elements had not been axially displaced in relation to each other, as a certain material thickness is required for the inner bearing ring/ring gear.
The vehicle according to the second aspect of the present invention comprises a wheel hub unit according to the first aspect of the present invention. The wheel hub unit according to the first aspect of the present invention may be beneficial to use in a work machine, or in a truck, a bus or a car.
According to one exemplary embodiment, said vehicle is a work machine, such as a wheel loader.
According to one exemplary embodiment, said wheel hub unit is provided in a rim of said vehicle, and wherein the rolling elements of the bearing are closer to a center of the rim, as seen in the width direction of said rim, than the engagement area. It is beneficial, in terms of bearing load and torque subjected to the bearing and thereby the expected life length of the bearing, to provide the bearing center close to the axial center of the rim that the wheel hub unit is connected to. It is therefore more beneficial to displace the engagement area along the axial direction of the rim.